Lithium-ion batteries (LIB) are widely used in electronic devices, electric vehicles, and for the storage of renewable energies such as photovoltaic and wind energies, among others. LIBs allow the storage of this energy for later use, being it possible to adapt them to different energy demand conditions.
The current research work on LIBs is focused on obtaining high capacity anodes based on silicon (Si), since the theoretical capacity of said anodes is 3579 mAhg−1, being significantly higher than that of graphite, which is more commonly used: 372 mAhg−1. However, it is known that Si undergoes a significant process of volumetric expansion that causes a progressive pulverization and disconnection of electrical contact. This results in a loss of anode capacity during the first cycles of a LIB operation.
The Si-metal-based anodes in a LIB undergo a volumetric expansion of approximately 300%, due to the formation of an alloy of general formula LixSiy. On the other hand, graphite undergoes a smaller expansion, of approximately 7%, as a consequence of an intercalation mechanism of Li ions in the graphite layers. In the first case, the negative effect of this expansion has been partially solved using Si nanoparticles encapsulated in conductive carbon, or by reduction of pre-synthesized SiO2 composites by magnesiothermal reduction.
Patent application US 2017/260057 describes a process for the manufacture of nanoparticles of formula SiOx, where x is comprised between 0.8 and 1.2, by means of a fusion reaction between SiO2 and Si, at a temperature of at least 1410° C.
The disadvantage of such strategies is the high cost of the process, since the reduction of SiO2 to Si has a high activation energy, and is therefore expensive. Additionally, the volumetric expansion of the Si particles thus formed represents a drawback on an industrial scale.
Additionally, the charge/discharge capacity should be improved by an adequate ionic conductivity during the electrochemical process of Li ion migration. To this end, the ionic and electrical conductivities of the electrode materials must be improved. In this way, the high specific capacity could be maintained, even at high current densities.
Patent applications CN 106159222 and CN104701496 describe anodes for a LIB comprising a carbonaceous structure of high electrical conductivity, as well as Co and Sn nanoparticles. Although these anodes are manufactured from a material based on SiO2, said material is subsequently removed from the anodes. Application CN 104528740 is directed to a composite material comprising SiO2 and carbon, with a carbon content of less than 20%. None of these documents teaches or suggests the anodes and manufacturing methods of the present invention.
SiO2-based materials are attractive alternatives for the manufacture of Si-based anodes, since silica is one of the most abundant elements in Earth's crust and since SiO2 clays with complex porous nanostructures are well known. The synthesis of nanoporous materials from SiO2 is generally simple and inexpensive. In addition, these compounds could be used as a model material for complex natural clays, which could be used to store energy at a reduced cost. However, the main drawback of silica is the insulation characteristics thereof. Electron conduction is not possible with pure SiO2, thus limiting possible reduction to Si and other silicon products. The formation of said other products, in particular of LixSiy compounds, is decisive, since they provide ionic conductivity and allow limiting the volumetric expansion during the charging and discharging processes of a LIB.
There is therefore a need to provide an anode for a LIB that has improved electrical conductivity and volumetric expansion characteristics, and the manufacturing process of which is economically advantageous, compared to the existing alternatives of the prior art.